Corrosion resistant alloys

ABSTRACT

AN ALLOY WHICH IS RESISTANT TO CORROSION BY BOTH OXIDIZING AND REDUCING SULFURIC ACID SOLUTIONS OVER A WIDE RANGE OF ACID STRENGHTS. THE ALLOY CONSIST OF BETWEEN ABOUT 36% AND ABOUT 46% BY WEIGHT NICKEL, BETWEEN ABOUT 33% AND ABOUT 42.06% BY WEIGHT CHROMIUM, BETWEEN ABOUT 2.94% AND ABOUT 7.84% BY WEIGHT MOLBYDENUM, BETWEEN ABOUT 1.95% AND ABOUT 5.18% BY WEIGHT COPPER, UP TO ABOUT 0.12% BY WEIGHT CARBON, UP TO ABOUT 1.50% BY WEIGHT SILICON, UP TO ABOUT 2.50% BY WEIGHT MANGANESE, UP TO ABOUT 2% BY WEIGHT TITANIUM, UP TO ABOUT 4% BY WEIGHT NIOBIUM PLUS TANTALUM, UP TO ABOUT 0.01% BY WEIGHT BORON, AND THE BALANCE ESSENTIALLY IRON. MOST OF THE ALLOYS OF THE INVENTION ARE READILY WELDABLE, MACHINABLE, AND WORKABLE. THOSE WHICH CANNOT BE READILY WORKED ARE GENERALLY HARD AND WEAR-RESISTANT.

United States Patent US. Cl. 75-122 Claims ABSTRACT OF THE DISCLOSURE Analloy which is resistant to corrosion by both oxidizing and reducingsulfuric acid solutions over a wide range of acid strengths. The alloyconsists of between about 36% and about 46% by weight nickel, betweenabout 33% and about 42.06% by weight chromium, between about 2.94% andabout 7.84% by weight molybdenum, between about 1.95% and about 5.18% byweight copper, up to about 0.12% by weight carbon, up to about 1.50% byweight silicon, up to about 2.50% by weight manganese, up to about 2% byweight titanium, up to about 4% by weight niobium plus tantalum, up toabout 0.01% by weight boron, and the balance essentially iron. Most ofthe alloys of the invention are readily weldable, machinable, andworkable. Those which cannot be readily worked are generally hard andwear-resistant.

BACKGROUND OF THE INVENTION This invention relates tocorrosion-resistant alloys and more particularly to weldable, machinableand workable alloys which are resistant to corrosion by both oxidizingand reducing sulfuric acid solutions over a wide range of acidstrengths.

Sulfuric acid is an ubiquitous industrial reagent which is generallyvery corrosive to most metals. The corrosivity of sulfuric acid to anygiven metal, however, varies widely with the strength of the acid, thetemperature of the acid environment, and the nature and concentration ofvarious contaminants. Because of the wide ranging uses for sulfuricacid, industrial process streams may be found which run the gamut ofsulfuric acid concentrations; which must be handled from temperaturesbelow room temperature up to the boiling point of the acid; and whichcontain an extensive variety of contaminants, e.g., other acids andsalts.

For purposes of analyzing and predicting their corrosive effect onmetals, acids and other corrosive agents are commonly classified aseither oxidizing or reducing." A reducing medium is generally defined asone which includes no component more oxidizing than the hydrogen ion orhydronium ion while an oxidizing medium is one which does contain such acomponent. Sulfuric acid, along with such other common materials ashydrochloric acid, acetic acid, phosphoric acid, aluminum chloride,hydrobromic acid, and hydrofluoric acid, is normally a reducing medium.At concentrations above approximately 85% by weight, however, sulfuricacid becomes an oxidizing agent. If its temperature is elevated,sulfuric acid may be oxidizing at even lower concentrations. Thus, a 60%by weight sulfuric acid solution becomes oxidizing at temperatures inexcess of 150 F. Even lower concentrations of sulfuric acid can bemoderately to strongly oxidizing when they contain various oxidizingacids and salts. Among the most common solutions of this type are theso-called mixed acids, which are mixtures of sulfuric acid and nitricacid used in organic nitration processes. Other oxidizing materials,some of which may be found in industrial sulfuric acid streams, includehydrogen peroxide, ferric sulfate, silver nitrate, potassium nitrate,sodium nitrate, copper sulfate,

ice

potassium permanganate, sodium dichromate, chromic acid, calciumchloride, mercuric chloride, aqua regia, sodium hypochlorite, ferricchloride, and cupric chloride.

Because of this variety in the character of various industrial sulfuricacid streams, there are relatively few metals available which can besaid to be generally useful in sulfuric acid service. For example, ametal which quite satisfactorily resists the corrosive effect ofreducingtype sulfuric acid solutions may fail rapidly if a smallproportion of an oxidizing agent is present, or if the temperature ofthe system is elevated well above room temperature. Many alloys whichresist dilute sulfuric acid solutions are completely unsuitable forsulfuric acid solutions having concentrations in excess of 60% or 70% byweight. Certain other alloys are available which are highly resistant toa wide range of sulfuric acid solutions, including concentrated sulfuricacid but, for the most part, such of these alloys as have been availablehave suffered from undesirable mechanical or other properties. Commondrawbacks of such alloys have been poor machinability and weldability,with poor workability being an almost universal problem with thesealloys, i.e., essentially none of these alloys can be feasibly producedin wrought form.

SUMMARY OF THE INVENTION Among the several objects of the presentinvention, therefore, may be noted the provision of novel alloys whichare resistant to sulfuric acid over a wide range of concentrations; theprovision of such alloys which are resistant to sulfuric acid up to 200F. or higher; the provision of such alloys which are resist-ant tosulfuric acid solutions containing oxidizing contaminants; and theprovision of such alloys which are weldable, machinable and workable.Other objects and features will be in part apparent and in part pointedout hereinafter.

The present invention is therefore directed to an alloy resistant tocorrosion by both oxidizing and reducing sulfuric acid solutions over awide range of acid strengths, consisting essentially of between about36% and about 46% by weight nickel, between about 33% and about 42.06%by weight chromium, between about 2.94% and about 7.84% by weightmolybdenum, between about 1.95% and about 5.18% by weight copper, up toabout 0.12% by weight carbon, up to about 1.50% by weight silicon, up toabout 2.50% by weight manganese, up to about 2% titanium, up to about 4%by weight niobium plus tantalum, up to about 0.01% by weight boron, andthe balance essentially iron.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The alloys of the presentinvention are suitable as materials of construction for equipment usedin reducingtype sulfuric acid solutions at temperatures up to theboiling point. As a result of the high proportion of chromium containedin these alloys, the alloys also exhibit good corrosion resistance tohigh temperature concentrated sulfuric acid and to sulfuric acidcontaminated with oxidiz ing agents such as nitric acid. Except in therelatively narrow composition ranges where the alloy structure is notsufficiently austenitic, the alloys of the invention are readilyweldable and machinable and, most importantly, are possessed ofsufiicient ductility to be shaped and processed by hot or cold-working.The alloys of the invention which are not readily workable generallypossess the alternative advantageous properties of high hardness andwear resistance. In either case, these alloys are adapted for use asmaterials of construction for a wide variety of chemical and otherindustrial process equipment.

The essential constituents of the alloys of the invention are:

Percent by weight Nickel 36 to 46 Chromium 33 to 42.06 Molybdenum 2.94to 7.84 Copper 1.95 to 5.18

Carbon Up to 0.12 Silicon Up to 1.50 Manganese Up to 2.50 Titanium Up to2 Niobium+tantalum Up to 4 Boron Up to 0.01 Iron Balance lybdenum andother constituents for a particular alloy are established, the balanceof the alloy is desirably constituted by iron, since it is abundant,inexpensive, and generally lends good mechanical properties to thealloy. If enough iron is included so as to modify the austeniticstructure of the alloy, however, fabricability is adversely affected. Itis, therefore, preferred that the iron content be maintained below theproportion which would introduce non-austenitic characteristics to thealloy microstructure.

The alloys of the invention are prepared by conventional methods ofmelting and no special conditions such as controlled atmospheres arerequired. In preparing the alloys, the constituents of a melting furnacecharge need not be of any particular type. Thus, raw materials such asremelt scrap, copper scrap, ferro alloys such as ferrosilicon andferromanganese and other commercial melting alloys may be used.

The following examples illustate the invention.

Example 1 100 lb. heats of seven different alloys were prepared inaccordance with the invention. Each of these heats was then melted in a100 lb. high frequency induction furnace. The compositions of thesealloys are set forth in Table 1, with the balance in each case beingiron.

TABLE 1.PERCENTAGE BY WEIGHT OF ALLOYING ELEMENTS Cr M0 Cu O Si Mn Ti Nb+Ta B Silicon enhances the corrosion resistance of the alloys to allstrengths of sulfuric acid, and a small proportion of silicon isdesirably present. However, large proportions of silicon tend to renderthe alloys hard and brittle, with poor welding and machiningcharacteristics. It is preferable, therefore, to maintain the siliconcontent below about 1.50% to insure the workability of the alloys.

Manganese is desirably present because of its deoxidizing capabilities.Up to 8-l0% of manganese can be tolerated in these alloys withoutadverse effect on either corrosion resistance or mechanical properties.If more than about 2.50% by weight manganese is present, however, enoughmanganese oxide may be present to cause attack on a furnace lining or amolding sand. Thus, the maximum manganese content of the alloys shouldnot exceed about 2.50% by weight.

A small amount of boron improves the fabricability of the alloys. Thus,as much as 0.01% boron may be present. Higher percentages of boron areundesirable, since significantly higher proportions tend to harden thealloys or to adversely aifect their corrosion resistance.

Up to about 2% titanium and up to about 4% niobium plus tantalum areuseful in stabilizing any excess carbon that may be present in thealloys. These elements are also relatively corrosion-resistant andcontribute as such to the corrosion resistance of the alloys. Titaniumadditionally contributes to the fabricability of the alloys.

A preferred embodiment of the alloys of this invention contains betweenabout 40% and about 44% by weight nickel, between about 33% and about byweight chromium, between about 3% and about 4% by weight molybdenum, andbetween about 3% and about 4% by weight copper. Alloys in this rangecombine particularly high corrosion resistance with a high degree oftoughness, ductility and workability.

Normally, the alloys of the invention include a certain proportion ofiron, up to about 25% by weight. Once the appropriate proportions ofnickel, chromium, copper, mo-

Two standard physical test blocks and three corrosion test bars wereprepared from each heat. One of the physical test blocks from each alloywas solution-annealed at 1950 F. for three hours and then oil quenched.The physical properties of the alloys, in both the annealed and theas-cast state, were measured. The as-cast physical properties of arepresentative number of these alloys are set forth in Table 2, and thephysical properties of two of the same alloys after annealing are setforth in Table 3. The magnetic permeability of these alloys is generallyless than about 1.02, in either as-cast or annealed condition.

TABLE 2.PHYSIOAL PROPERTIES OF ALLOYS, AS-CAST Tensile Yield strength,strength, Percent Brinell Alloy p.s.i. p.s.i. elongation hardness TABLE3.PHYSICAL PROPERTIES OF ALLOYS, AFTER SOLUTION ANNEALING The corrosiontest bars were also annealed for thirty minutes at 1950 F. and oilquenched prior to machining into 1 /2 diameter x A high discs having adiameter hole in the center. Twelve to fourteen discs Were obtained foreach alloy. As machined, these discs had a surface roughness of about 32microinches. A number of the discs of each alloy were electropolished toreduce surface roughness to about 4 microinches.

Both rough and electropolished discs were used in the comparativecorrosion tests described hereinafter, comparing the performance of thealloys of the invention with a number of commercially available alloys.Because of the relatively short duration of the corrosion tests,significant differences were expected between the observed corrosionrates of rough and polished sample discs, and this is the reason forwhich both types of surfaces were tested. It is well-known in the artthat rough surfaces often have substantially higher initial corrosionrates than do polished surfaces, especially those which areelectropolished. This phenomenon is variously ascribed to the higheractual contact area presented by a rough surface, the higher chemicalactivity of a rough surface, and the greater difficulty in forming aprotective film on a rough surface, where corrosion resistance dependson the presence of such a film. It has also been posited that machiningoperations, such as those involved in preparing sample discs, can causework-induced phase changes at the metal surface. In the case of thealloys of this invention, such a phenomenon may alter the austeniticcharacter of the alloy surface and thus reduce surface corrosionresistance. Electropolishing removes this work-transformed margin andexposes the unaifected subjacent area.

The compositions of the commercially available alloys which were used inthe following corrosion tests and the respective trade designationsunder which they are marketed are set forth in Table 4.

After precisely six hours, the sample discs were removed from theboiling acid solution and cleaned of corrosion products. Most sampleswere cleaned sufficiently with a small nylon bristle brush and tapWater. Those samples on which the corrosion product was too heavy forremoval with a nylon brush were cleaned with a 1:1 solution ofhydrochloric acid and water. After the corrosion products had beenremoved, each disc was again weighed to the nearest 10,000th of a gram.The corrosion rate of each disc, in inches per year, was calculated bythe following formula in accordance with ASTM specification G1-67.

where R-, =corrosion rate in inches per year W =original weight ofsample W =final weight of sample A=area of sample in square centimetersT=duration of test in years D=density of alloy in g./ cc.

Results of this corrosion test are set forth in Table 5.

TABLE 4.COMMERCIAL ALLOYS UTILIZED IN COMPARATIVE CORROSION TESTS Ni G!M0 Cu Si W 0 Mn 00 Others Hastelloy A... 0.70 0. 08 1. 00 Hastelloy B0.70 0. 04 0. 70 Hastelloy C 0.70 0.11 0. 70 Hastelloy D 9. 0 0.10 1. 00Hastelloy 0. 50 0. 04 1. 50 Illium G 0.65 0.20 1.25 Illium IL.-- 0. 700.05 1. 25 Illium 98..-- 0.7 0. 05 1. 25 Worthite-- 3. 50 0. 07 1. 00Inconel 625 0. 0.08 0.30 Duriron 14. 5 0.50 0.50

RIIA 0.70. 0.04 1.00 Ni-O-N e1 0. 0. 05 0. 50 Marker SN 42- 0. 70 0. 050.70

F 8M 1.00 0.05 1.00 CF 8 0.50 0.07 0.50 Monel. 0.10 0.15 1. 00 Inconel0. 25 0. 08 0. 25 Stellite No. 25--. 0. 50 0.10 0.70 Carp enter 20 4Carpenter 20 Cb3 32. 5 20 2.5 35 0.03 0.05 CD4M Cu 25 2 3 0. 03 0.5

Example 2 TABLE 5 Comparative corrosion tests were conducted in aboiling mixed acid solution containing 5% by weight nitric acid and 10%by weight sulfuric acid.

Disc samples of Hastelloy B, Carpenter 20, nickel and Monel wereprepared having the same dimensions as the discs prepared in Example 1.Residual machining oil and dirt were removed from all of the samplediscs by cleaning them with a small amount of carbon tetrachloride. Thediscs were then rinsed in Water and dried. Surface roughness of thesediscs was on the order of 4-10 microinches.

Each disc was weighed to the nearest 10,000th of a gram and suspended ina beaker containing a sufiicient amount of boiling 10% sulfuric/ 5%nitric acid solution so that the entire sample was surrounded. Thesample was suspended by means of a thin platinum wire hooked through thecenter hole of the disc and attached to a glass rod which rested on thetop of the beaker. To insure the exposure of the discs to mixed acidsolutions of substantially constant strength, frequent substitutions ofbeakers containing fresh boiling acid were made.

[Corrosion rates in boiling 10% H2304 plus 6% HNOa solution] Loss ininches I Not resistant.

Example 3 Comparative corrosion tests were conducted in boiling 10%sulfuric acid solution. Sample discs were prepared and tested in themanner described in Example 2, except that the test solution was boiling10% sulfuric acid. The results of this test are set forth in Table 6.

TABLE 6 [Corrosion rates in boiling 10% H2804 solution] Loss in inchesof penetration per year, i.p.y.

Surface roughness Alloy number:

1,025 32 microin.

971d- I do 4-10 microin.

Example 4 TABLE 7 [Corrosion rates in 65-68% HNO; solution at 150 F.]

Loss in inches of penetration per year, i.p.y.

Surface roughness Alloy number:

Hastelloy A- Hastelloy B.

I No resistance.

Example Comparative corrosion tests were conducted in 10% sulfuric acidsolution at 176 F. Sample discs were prepared and tested in the mannerdescribed in Example 4, except that a 10% sulfuric acid solution wasutilized and the temperature was maintained at 176 F. The results ofthis test are set forth in Table 8.

TABLE 8 [Corrosion rates in 10% H28 04 solution at 176 F.]

Loss in inches Surface of penetration roughness per year, i.p.y.

Alloy number:

960 32 microin- 0. 00735 961 -d0 0. 00486 971 -do- 0. 00081 1.025 -(10.0. 00540 CD4M Cu 4-10 microin- 0. 004 Hastelloy A .do- 0. 0036 HastelloyB .110. 0.003 Hastelloy C .do- 0. 003 Hastelloy D d0 0. 005 Carpenter 20.do. 0. 005 Carpenter 20Cb3 -410- 0. 0045 M el (1 0. 009 0. 012 0. 0630.020 0. 0051 0. 004 4. 5 0. 197

Example 6 Comparative corrosion tests were conducted in boiling 25%sulfuric acid solution. Sample discs were prepared and tested in themanner described in Example 2, except that boiling 25 sulfuric acid wasused as the test solution. The results of this test are set forth inTable 9.

TABLE 9 [Corrosion rates in boiling 25% H2804 solution] Loss in inchesof penetration per year, i.p.y.

Surface roughness Alloy number:

32 microin- 0. 1620 1 About 1.0.

Example 7 Comparative corrosion tests were conducted in 25% sulfuricacid solution at 176 F. Sample discs were prepared and tested in themanner described in Example 4, except that a test solution of 25%sulfuric acid was utilized and temperature was maintained at 176 F.Results of this test are set forth in Table 10.

TABLE 10 [Corrosion rates in 25% H2804 solution at 176 F.]

Loss in inches Surface of penetration roughness per year, i.p.y.

Alloy number:

960 32 microin.. 0. 00378 96l d0 0.0000 971--.. -do- 0. 00108 972- d0 0.00594 1, 0 --d0..- 0. 0041 Hastelloy A -IO mier01n 0. 020 Illium R-- 0.007 Carpenter 20 0. 020 Carpenter 20Cb3 .do. 0. 011 -do- 0. 010

CD4M Cu do 0.200

Example 8 Comparative corrosion tests were conducted in 25% sulfuricacid solution at room temperature. Sample discs were prepared and testedin the manner described in Ex ample 4, except that 25 sulfuric acid atroom temperature was used as the test solution. The results of this testare set forth in Table 11.

Example 9 Comparative corrosion tests were conducted in 93% sulfuricacid solution at 210 F. Sample discs were prepared and tested in themanner described in Example 4, except that 93% sulfuric acid solution at210 F. was used as the test solution. Results of this test are set forthin Table 12.

TABLE 12 [Corrosion rates in 93% H2804 solution at 210 F] Loss in inchesSurface of penetration roughness per year, i.p.y.

Alloy number:

960 32 microin..

Hastelloy F .I-

Example Comparative corrosion tests were conducted in 10% hydrochloricacid solution at room temperature. Sample discs were prepared and testedin the manner described in Example 4, except that 10% hydrochloric acidat room temperature was used as the test solution. The results of thistest are set forth in Table 13.

TABLE 13 [Corrosion rates in 10% E01 solution at room temperature] Lossin inches of penetration per year. i.p.y.

Surface roughness Example 11 Comparative corrosion tests were conductedin 20% hydrochloric acid solution at room temperature. Sample discs wereprepared and tested in the manner described in Example 4, except that20% hydrochloric acid at room temperature was used as the test solution.Results of this test are set forth in Table 14.

TABLE 14 [Corrosion rates in 20% HO] solution at room temperature] Lossin inches Surface of penetration roughness per year. i.p.y.

Alloy number:

961..-"; 32 microin- 0. 0233 971.-. -do 0. 0187 Hastelloy D- 4-10microin.-. 0. 026 8 do 1. 22

10 Example '12 Corrosion tests were conducted in 50% sulfuric acidsolution at 176 F. Sample discs were prepared and tested in the mannerdescribed in Example 4, except that 50% sulfuric acid solution at 176 F.was used as the test solution. Results of this test are set forth inTable 15.

TABLE 15 [Corrosion rates in 50% H2SO4 solution at 176 F.]

Loss in inches of penetration per year, i.p.y.

Surface roughness:

Alloy number Example 13 Corrosion tests were conducted in 75% sulfuricacid at 176 F. Sample discs were prepared and tested in the mannerdescribed in Example 4, except that 75% sulfuric acid at 176 F. was usedas the test solution. Results of this test are set forth in Table 16.

TABLE 16 [Corrosion rates in 75% H2804 solution at 176 F.]

Loss in inches of penetration per year, i.p.y.

Surface roughness:

Alloy number Example 14 Corrosion tests were conducted in 93% sulfuricacid at 176 F. Sample discs were prepared and tested in the mannerdescribed in Example 4, except that 93% sulfuric acid at 176 F. was usedas the test solution. Results of this test are set forth in Table 17.

TABLE 17 [Corrosion rates in 93% H2804 solution at 176 F.]

Loss in inches of penetration per year, i.p.y.

Surface roughness Alloy number Example 15 Comparative corrosion testswere conducted in boiling 40% sulfuric acid. Sample discs were preparedand tested in the manner described in Example 2, except that boiling 40%sulfuric acid was used as the test solution. Results of this test areset forth in Table 18.

TABLE 18 [Corrosion rates in boiling 40% H2804 solution] Loss in inchesSurface of penetration roughness per year, i.p.y.

Alloy number:

960 4 microin 0.0000 961--. 0. 0043 971... 0. 0000 1, 2 0.- 0.0000Carpenter 200133 4-10 micrcin- 0. 040

Example 16 Comparative corrosion tests were conducted in boiling 50%sulfuric acid. Sample discs were prepared and tested in the mannerdescribed in Example 2, except that boiling 50% sulfuric acid was usedas the test solution. Results of this test are set forth in Table 19.

TABLE 19 [Corrosion rates in boiling 50% H2804 solution] Loss in inchesIn view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above products without departingfrom the scope of the invention, it is intended that all mattercontained in the above description shall be interpreted as illustrativeand not in a limiting sense.

What is claimed is:

1. An alloy resistant to corrosion by both oxidizing and reducingsulfuric acid solutions over a wide range of acid strengths, consistingessentially of between about 36% and about 46% by weight nickel, betweenabout 33% and about 42.06% by weight chromium, between about 2.94% andabout 7.84% by weight molybdenum, between about 1.95% and about 5.18% byweight copper, up to about 0.12% by weight carbon, up to about 1.50% byweight silicon, up to about 2.50% by weight manganese, up to about 2% byweight titanium, up to about 4% by weight niobium plus tantalum, up toabout 0.1% by weight boron, and the balance essentially iron.

2. An alloy as set forth in claim 1 having a microstructure which issubstantially austenitic so that the alloy is readily workable.

3. An alloy as set forth in claim 1 wherein the nickel content isbetween about 40% and about 44% by weight, the chromium content isbetween about 33% and about 35% by weight, the molybdenum content isbetween about 3% and about 4% by weight and the copper content isbetween about 3% and about 4% by weight.

4. An alloy as set forth in claim 3 containing about 42% by weightnickel, about 34% by weight chromium, about 3.2% by weight molybdenum,and about 3.6% by weight copper.

5. An alloy as set forth in claim 1 containing about 43% by weightnickel, about 42% by weight chromium, about 4.9% by weight molybdenum,and about 3.9% by weight copper.

6. An alloy as set forth in claim 1 containing about 46% by weightnickel, about 35% by weight chromium, about 7.8% by weight molybdenum,and about 5.2% by weight copper.

7. An alloy as set forth in claim 1 containing about 37% by weightnickel, about 33% by weight chromium, about 3.8% by weight molybdenum,about 3.3% by wei-ght copper, about 1.7% by weight silicon, about 2.0%by weight manganese, about 0.08% by weight titanium, and about 0.005% byweight boron.

8. An alloy as set forth in claim 1 containing about by weight nickel,about 41% by weight chromium, about 2.9% by weight molybdenum, and about2.0% by weight copper.

9. An alloy as set forth in claim 1 containing about 43% by weightnickel, about 38% by weight chromium, about 3.6% by weight molybdenum,and about 3.2% by weight copper.

10. An alloy as set forth in claim 1 containing about 44% by weightnickel, about 34% by weight chromium, about 3.4% by weight molybdenum,and about 2.6% by weight copper.

References Cited UNITED STATES PATENTS 3,552,950 1/1971 Rundell -1712,553,330 5/1951 Post 75-122 3,356,542 12/1967 Smith 75-122 3,574,6124/1971 Maness 75-171 3,582,318 6/1971 Szumachowski 75-171 HYLAND' BIZOT, Primary Examiner US. Cl. X.R.

